How do I paint a texture onto an already textured object?
Repeated Image Mapping

The slot named Textures near the cursor in the Tool Tab is relative to the Brush



The slot in where you can choose which is the acticve texture to paint onto can be found in the Slot Tab in the Slot panel. The active texture is the one highlited with blue color.



As you can see on the right you are probably painting a texture with a brush that paint other textures, maybe sometime the same, and may be one of the causes you have repeating features spreading all around.

But the main cause of that relies on the Repeating settings of your Skin texture.



Those values alter how the texture is placed and sized on the UV space. You must set them to 1 an 1 to get the UV unwrapped island to stay in place.

If you want to paint just plain colors, remove Brush Texture by hitting the X button. If you want to paint texture from an image, be sure to use diffrent textures.